Headbox of a paper machine or equivalent

ABSTRACT

The invention relates to a headbox of a paper machine or equivalent. The headbox comprises in its connection cleaning tubes ( 11   a   1   , 11   a   2  . . . ), by means of which stock is separated into accept and reject, the accept being passed forward in the headbox and further onto a forming wire (H 1 ).

[0001] The invention relates to a headbox of a paper machine or equivalent.

[0002] In the papermaking process, so far there are no other alternatives than hydrocyclones for removal of small heavy particles, which hydrocyclones operate at present at a low fibre consistency of about 1.0% with sufficient efficiency.

[0003] Also, in papermaking in the manufacture of a web/base paper, there has been no success in finding a solution for the increase of consistency in order that sufficient strength and uniform quality should be achieved for paper. To achieve competitiveness it should be possible to simplify processes and to increase consistencies in the entire stock preparation and papermaking process before the headbox. Today, hydrocyclones/sand separation are placed in stock preparation and in the short circulation, which prevents the consistency from being increased in stock preparation and in the short circulation to a pumping consistency of, for example, 3-5%. The purpose of the invention is to alleviate this problem, i.e. when sand removal and a dilution headbox are combined, the screening consistency of the stock in the short circulation can be easily raised to a consistency of 3-4% and dilution to a web-forming consistency is performed just before an integrated hydrocyclone headbox in accordance with the invention. In other words, hydrocyclone cleaning can be placed between the dilution stage of a dilution headbox and the headbox proper. At this point there is the lowest consistency of the stock circulation before web-forming, because a dilution headbox dilutes the stock by 7-20%. Thus, the headbox consistency can be kept suitable for papermaking but the short circulation consistency can be increased to a higher screening and pumping consistency and, in that part of the process, it is possible to achieve saving on energy and simplification of the processes. In that connection, it is also possible to increase the web-forming consistency to over 1%. By means of this invention, the lowest consistency of the main stream in the stock+paparmaking line is in the hydrocyclone headbox.

[0004] In the hydrocyclone headbox, the first stage of centrifugal cleaning is placed in the headbox before a turbulence generator. As hydrocyclones it is possible to use conventional devices as modified to a higher pressure. However, a more attractive alternative is to build hydrocyclones inside the headbox in place of a conventional distribution tube bank. In that connection, the tube diameters of the tube bank shall be enlarged by about 20-50% in order to accommodate an accept duct inside a tube.

[0005] By the paper machine or equivalent is meant a paper, board and tissue machine or a pulp drying machine.

[0006] The headbox of a paper machine or equivalent according to the invention is characterized by what is stated in the claims.

[0007] In the following, the invention will be described with reference to some advantageous embodiments of the invention shown in the figures of the appended drawings but the invention is not meant to be limited to said embodiments only.

[0008]FIG. 1A shows a so-called hydrocyclone headbox of a paper machine or equivalent in accordance with the invention as well as the associated short circulation of the stock.

[0009]FIG. 1B is a longitudinal sectional view of a hydrocyclone headbox associated with the system in accordance with the embodiment of FIG. 1A.

[0010]FIG. 1C shows a section I-I from FIG. 1B.

[0011]FIG. 1D is a separate view of the structure of a cleaning tube associated with the hydrocyclone headbox in accordance with the invention.

[0012]FIG. 2A shows a second embodiment of the invention in which the hydrocyclone headbox does not comprise attenuation but in which the structure otherwise corresponds to the embodiment of FIGS. 1A-1D.

[0013]FIG. 2B is a longitudinal sectional view of a hydrocyclone headbox associated with the system illustrated in FIG. 2A.

[0014]FIG. 2C shows a section II-II from FIG. 2B.

[0015]FIG. 2D shows one advantageous structural form of a cleaning tube associated with the hydrocyclone headbox illustrated in FIG. 2B.

[0016]FIG. 3A shows an embodiment of the invention which is primarily associated with the system of FIGS. 1A-1D, in which the hydrocyclone headbox comprises an inlet header for the stock as well as an inlet header for dilution water. FIG. 3A is a longitudinal sectional view of the hydrocyclone headbox and FIG. 3B shows the structure of a cleaning tube associated with the headbox of FIG. 3A.

[0017]FIG. 4 shows an embodiment of the invention in which a dilution flow and a thick stock flow are combined before they are passed to a cleaning tube.

[0018]FIG. 1A shows a headbox 10 of a paper machine in accordance with the invention comprising in its connection cleaning tubes 11 a ₁, 11 a ₂ . . . of a first hydrocyclone cleaning step PuI of a hydrocyclone installation 11. In the invention it is possible to speak of a novel type of headbox, which in this patent application is called a hydrocyclone headbox. FIG. 1A shows a short circulation 12 associated with the headbox 10 in accordance with the invention. The stock is passed from the headbox 10 through the cleaning tube bank 11 a ₁, 11 a ₂ . . . of the first step PuI of the hydrocyclone installation 11 and through an intermediate chamber 30 and a turbulence generator 31 into a slice cone 32 and further onto a forming wire H₁. Wire water is passed from a wire section 13 to a dilution circulation 14, in which a pump P1 transfers the dilution liquid through a screen 15 and a duct 16 further to a dilution liquid inlet header J₂ of the headbox 10. The dilution inlet header J₂ comprises a return duct 28 for circulation water. A valve V₂ controls the flow of the circulation water. The duct 28 is connected with a duct 27, which leads from a reject inlet header J₃. The reject from the screen 15 is passed from the screen 15 further through a duct 17 to screening 18 to a duct 25 and further through another screen 19 and an accept duct 20 to an accept duct 21 of a second step PuII of the hydrocyclone installation 11, which accept duct 21 leads to a thick stock duct 22, which comprises a pump P₂ which causes the stock to circulate through a screen 23 to a duct 24 and to a stock inlet header J₁, from which there is a return circulation through a duct 26 to the duct 22 and to the suction side of the pump P₂. The reject is passed from the headbox 10 further to the duct 27 of the second step PuII in the hydrocyclone installation 11 and through a valve V₁ which is situated in the duct 27 and by which the flow is regulated. The accept from the second step is passed further to the duct 21 and further back to the stock duct 22 situated after a thick stock tank 29. The reject from the second step PuII is passed further to, for example, screening. The reject from the screen 23 situated in the duct 22 is passed to the duct 25, which is connected to the screen 19.

[0019]FIG. 1B is a longitudinal sectional view of a hydrocyclone headbox 10 associated with the embodiment of FIG. 1A in accordance with the invention and comprising in its connection a dilution inlet header J₂. Dilution water is distributed from the inlet header J₂, while regulated by valves V₃, to cleaning tubes 11 a ₁, 11 a ₂ . . . . The arrangement shown in FIG. 1B in accordance with the invention comprises a stock inlet header J₁, from which stock is passed (arrow L₁) to the hydrocyclone of the hydrocyclone headbox 10, i.e. to hydrocyclone tubes 11 a ₁, 11 a ₂ . . . , from which the accept is passed further to an intermediate chamber 30 and farther to a turbulence generator 31 and further from the turbulence generator 31 to a slice cone 32 and further onto a forming wire H₁. The reject from the hydrocyclone tube bank 11 a ₁, 11 a ₂ . . . is passed further to a reject inlet header J₃ and therefrom to a second step PuII of a hydrocyclone installation 11 and further to circulation after screening carried out by the second step.

[0020]FIG. 1C shows the structure of the cleaning tube bank 11 a ₁, 11 a ₂ . . . as a section I-I from FIG. 1B. As shown in the figure, dilution water L₂ is passed through the inlet header J₂ and, in a corresponding manner, a stock flow L₁ is passed through the stock inlet header J₁. The flows passed from the inlet headers J₁ and J₂ are branched off to branch ducts a₁, a₂, a₃ . . . (arrow L₁) and e₁, e₂, e₃ . . . (arrow L₂), the stock flow and the dilution water passed through the a₁ duct and the e₁ duct being passed to cleaning tubes placed one upon the other, the flows passed to the ducts e₂ and a₂ being passed to cleaning tubes 11 a ₁, 11 a ₂ and 11 a ₃ placed one upon the other, respectively, and so on. The dilution inlet header J₂ tapers towards its end in the same way as the stock inlet header J₁. By this means, an even stock flow is provided from the inlet headers J₁ and J₂ to each duct a₁, a₂, a₃ . . . ; e₁, e₂, e₃ . . . and further to the corresponding cleaning tubes.

[0021]FIG. 1D is a separate view of the structure of the cleaning tube 11 a ₁ of the hydrocyclone device 11. In the structure of FIG. 1D, the thick stock is passed through the cleaning tube 11 a ₁ through an inlet end C₁ to the cleaning tube 11 a ₁ into a tube 33. The reject is passed out through the other end C₂ of the cleaning tube 11 a ₁. The accept is passed through a central flow duct f₁ of an inner sleeve 34 in the cleaning tube 11 a ₁ from the end C₁ of the cleaning tube 11 a ₁ to the intermediate chamber 30 and forwards in the headbox 10. In accordance with the invention, one dilution water duct C₁, C₂ . . . is connected to each cleaning tube 11 a ₁, 11 a ₂ . . . tangentially and, in a corresponding manner, the thick stock ducts a1, a₂ . . . are connected tangentially to the respective cleaning tubes 11 a ₁, 11 a ₂ . . . with an angular distribution of 180° with respect to the above-mentioned tangential inlet. In the embodiment of FIG. 1D, both the dilution water (arrow L₂) and the stock (arrow L₁) are passed into the cleaning tube 11 a ₁ from the end C₁.

[0022]FIG. 2A is a general schematic view of a second advantageous embodiment of the invention. FIG. 2B is a longitudinal sectional view of the headbox according to the embodiment of FIG. 2A.

[0023] The stock (arrow L₁) is passed from a stock inlet header J₁ to cleaning tubes 11 a ₁, 11 a ₂ . . . . The embodiment shown in FIGS. 2A-2D corresponds to that of FIGS. 1A-1D except that the stock is not diluted in the headbox. The stock is supplied to the cleaning tubes 11 a ₁, 11 a ₂ . . . as already diluted at a headbox consistency.

[0024] In the embodiment shown in FIG. 2A, the system comprises only a stock inlet header J₁. The cleaning tube bank in a first hydrocyclone cleaning step PuI of a hydrocyclone installation 11 is situated in the headbox 10 itself, as in the preceding embodiment. The stock is passed from a wire pit or a deaeration tank along a duct 22, while pumped by a pump P₂, to a screen 23, from which the accept is passed to a duct 24 and further to the stock inlet header J₁. There is a return circulation from the stock inlet header J₁ through a duct 26 to the suction side of the pump P2 to the duct 22. From the hydrocyclone headbox 10 there is a flow through a reject inlet header J₃ to a duct 27, which flow is regulated in the duct 27 by means of a valve V1. The duct 27 leads to a hydrocyclone of a second step PuII of the hydrocyclone installation 11, from which the accept is passed to a duct 21 and therefrom further to the duct 22, as shown in FIG. 2A.

[0025] As shown in FIG. 2B, stock is passed from the inlet header J₁ to each cleaning tube 11 a ₁, 11 a ₂, 11 a ₃ . . . . FIG. 2C shows a section II-II from FIG. 2B. As shown in FIGS. 2B and 2C, stock is passed from its inlet header J₁ to ducts a₁, a₂ . . . and from the duct a₁ to cleaning tubes 11 a ₁, 11 a ₂, 11 a ₃ which are situated one above the other at a certain width point of the headbox. Cleaning tubes 11 a ₄, 11 a ₅, 11 a ₆ are situated at the next width point and stock is passed into them through the duct a₂ from the inlet header J₁, which tapers towards its end in order that the stock flow into the cleaning tubes may be made even. As in the preceding embodiment, the accept from the cleaning tubes is passed to an intermediate chamber 30 and further to a turbulence generator 31 and further to a slice cone 32 and onto a forming wire H₁.

[0026]FIG. 2D shows the embodiment of the cleaning tube 11 a ₁. Stock is passed from the inlet header, as shown by the arrow L₁, to an inlet end C₁ of the cleaning tube 11 a ₁ between an outer tube 33 and an inner sleeve 34 of the cleaning tube, and the accept is passed through a duct f₁ inside the inner sleeve 34 further to the intermediate chamber 30. The reject is passed through the other end C₂ of the cleaning tube out of connection with the structure further to the reject inlet header and further to a hydrocyclone tube or equivalent of the second step PuII of the hydrocyclone installation 11. In the structure in accordance with the invention, each cleaning tube 11 a ₁, 11 a ₂ . . . comprises an outer tube 33 which advantageously has a conical shape, so that, when the stock flow L₁ is passed tangentially inside the outer tube 33 of the cleaning tube, it is brought into a spiraling motion, whereby the particles are separated, because of the centrifugal force in a manner known in itself, mainly in respect of their weight such that the coarsest particles are guided from the edges of the outer tube of the cleaning tube through the end C₂ to the reject inlet header and the finer material is passed through the flow duct f₁ of the central inner sleeve 34 as the accept to the intermediate chamber 30 and forwards in the headbox.

[0027]FIGS. 3A and 3B show another alternative for treatment of stock L₁ and dilution water L₂. A cleaning tube 11 a ₁ comprises further an outer tube 33 and an inner sleeve 34, and the stock and the dilution water are passed inside the cleaning tube 11 a ₁ to an end C₂ opposite to that of the inner sleeve 34 of the cleaning tube, opposite to the end C₁ where the inner sleeve 34 is located. The accept is passed through a flow duct f₁ of the central inner sleeve 34 from the end C₁ of the cleaning tube 11 a ₁ further to an intermediate chamber 30 and the reject from between the inner sleeve 34 and the outer tube 33 through the same end C₁ out of connection with the cleaning tube 11 a ₁. Both the dilution water and the stock are passed into the cleaning tube 11 a ₁ tangentially to the outer tube 33 of the cleaning tube 11 a ₁ and with an angular distribution of 180° with respect to each other.

[0028] In one embodiment in accordance with the invention, the stock components to be metered are cleaned at a consistency of 3-4% and they are metered to the hydrocyclone cleaning of the headbox, the accept from said cleaning being passed forwards to the slice part of the headbox. In that case, no machine screen is needed before dilution.

[0029]FIG. 4 shows an embodiment of the invention which corresponds to the embodiment of FIG. 3B except that a thick stock flow L₁ and a dilution flow L₂ from a duct t₁ are combined before they are passed to a cleaning tube 11 a ₁. Thus, in connection with all cleaning tubes 11 a ₁, 11 a ₂ . . . in this embodiment of the invention the dilution water (flow L₂) and the thick stock (flow L₁) are combined and the combined flow L₁+L₂ is passed to the cleaning tube 11 a ₁, 11 a ₂ . . . . As also in the preceding embodiments, the combined flow L₁+L₂ is brought into a spiral motion, whereby heavier particles are separated because of the centrifugal force from the side of the cleaning tube 11 a ₁, 11 a ₂ . . . , and the accept is passed through a central duct f₁ forwards in the headbox.

[0030] Within the scope of the invention, an embodiment is feasible in which from the individual hydrocyclone tubes there are at least two, preferably more flow ducts for the accept from each individual hydrocyclone tube. Thus, the accept flow from each individual cleaning tube is branched off to at least two, preferably more flow ducts and thereby to different tube rows of the headbox, for example, directly to different tube rows of the turbulence generator and/or to different tubes of the same row and/or to different rows in the height direction and/or to different rows in the width direction of the headbox. 

1. A headbox (10) of a paper machine or equivalent, characterized in that it comprises in its connection cleaning tubes (11 a ₁, 11 a ₂ . . . ), by means of which stock is separated into accept and reject, the accept being passed forward in the headbox and further onto a forming wire (H₁).
 2. A headbox as claimed in claim 1, characterized in that the headbox (10) comprises the cleaning tubes (11 a ₁, 11 a ₂ . . . ) of a first step (PuI) of a hydrocyclone installation (11).
 3. A headbox as claimed in the preceding claim, characterized in that the cleaning tubes (11 a ₁, 11 a ₂ . . . ) are situated one upon the other and adjacent to one another in the headbox of the paper machine such that at least a stock flow (L₁) from a stock inlet header (J₁) is passed into each cleaning tube, the accept being passed centrally within the cleaning tubes out of each cleaning tube, advantageously to an intermediate chamber (30) of the headbox and further to a turbulence generator (31) and further to a slice cone (32) and further onto the wire (H₁).
 4. A headbox as claimed in any one of the preceding claims, characterized in that each cleaning tube (11 a ₁, 11 a ₂ . . . ) comprises a flow duct (a₁, a₂ . . . ) for the stock from the stock inlet header (J₁) and advantageously also a flow duct (e₁, e₂ . . . ) for dilution water from a dilution water inlet header (J₂), and that the cleaning tube (11 a ₁, 11 a ₂ . . . ) comprises an internal inner sleeve (34) inside an outer tube (33), and that the reject is passed out of the end of the outer tube (33) and the accept is passed through a flow duct (f₁) situated centrally inside the inner sleeve (34) forwards in the headbox.
 5. A headbox as claimed in the preceding claim, characterized in that the dilution water is passed to an inlet end (C₁) of each cleaning tube (11 a ₁), which inlet end is situated in the adjacency of the inner sleeve (34), and that the reject is passed from an end (C₂) of the cleaning tube opposite to the above-mentioned end (C₁) further to a reject inlet header (J₃) and further to a second step (PuII) of the hydrocyclone installation (11).
 6. A headbox as claimed in any one of the preceding claims, characterized in that the dilution water inlet header (J₂) comprises in its connection control valves (V₃), by means of which the dilution flow is regulated into each cleaning tube (11 a ₁, 11 a ₂ . . . ).
 7. A headbox as claimed in any one of the preceding claims, characterized in that each cleaning tube (11 a ₁, 11 a ₂ . . . ) comprises an outer tube (33), which comprises, at least over part of its length, a conical portion to produce a spiraling flow inside the outer tube (33) of the cleaning tube (11 a ₁, 11 a ₂ . . . ).
 8. A headbox as claimed in any one of the preceding claims, characterized in that both the stock inlet header (J₁) and the dilution water inlet header (J₂) taper towards their ends and comprise a duct (26) for a circulation flow back to a thick stock duct (22) to the suction side of a pump (P₂).
 9. A headbox as claimed in any one of the preceding claims, characterized in that a duct (27) connected to the reject inlet header (J₃) is provided with a valve (V₁), which regulates the reject flow to the second step (PUII) of the hydrocyclone installation (11).
 10. A headbox as claimed in any one of the preceding claims, characterized in that the dilution headbox (J₂) comprises a duct (28) for a circulation flow, which duct comprises a valve (V₂) for regulating the dilution circulation flow to the duct (27) leading from the reject inlet header (J₃).
 11. A headbox as claimed in any one of the preceding claims, characterized in that there is a duct (16) for a dilution circulation (14) from a wire section, in which connection dilution water is pumped by means of a pump (P₁) through a screen (15) further to the duct 16 and further to the dilution inlet header (J₂).
 12. A headbox as claimed in claim 1, characterized in that hydrocyclone cleaning is arranged to form the last process stage of the short circulation before the forming of a slice jet taking place in the headbox, and there are two or more flow ducts from the hydrocyclone cleaning to the headbox proper.
 13. A headbox as claimed in claim 1, characterized in that a dilution flow (L₂) and a stock flow (L₁) are combined before passing them to the cleaning tubes (11 a ₁, 11 a ₂ . . . ). 